Deleting information

From a purely technical perspective, there is no such thing as a delete function on your computer. Of course, you can drag a file to the Recycle Bin and empty the bin, but all this really does is clear the icon, remove the file's name from a hidden index of everything on your computer, and tell Windows that it can use the space for something else. Until it actually does use that space, however, the space will be occupied by the contents of the deleted information, much like a filing cabinet that has had all of its labels removed but still contains the original files. This is why, if you have the right software and act quickly enough, you can restore information that you've deleted by accident, as discussed in Chapter 5: How to recover from information loss.

You should also keep in mind that files are created and insecurely deleted, without your knowledge, every time you use your computer. Suppose, for example, that you are writing a large report. It may take you a week, working several hours each day, and every time the document is saved, Windows will create a new copy of the document and store it on your hard drive. After a few days of editing, you may have unknowingly saved several versions of the document, all at different stages of completion.

Windows generally deletes the old versions of a file, of course, but it does not look for the exact location of the original in order to overwrite it securely when a new copy is made. Instead, it simply puts the latest version into a new section of the metaphorical filing cabinet mentioned above, moves the label from the old section to the new one, and leaves the previous draft where it was until some other program needs to use that space. Clearly, if you have a good reason to destroy all traces of that document from your filing cabinet, removing the latest copy is not going to be enough, and simply throwing away the label would be even worse.

Remember, too, that computer hard drives are not the only devices that store digital information. CDs, DVDs, USB memory sticks, floppy disks, flash memory cards from mobile phones and removable hard drives all have the same issues, and you should not trust a simple delete or rewrite operation to clear sensitive information from any of them.